1. Field of the Invention
The present invention relates to lamps and other illumination devices. More specifically, the invention relates to LED-based lamps using minimum power to illuminate a chosen area.
2. Related Art
In the field of illumination devices, there has long been a trade-off between brightness and power conservation. It is known that the use of light emitting diodes (LED's) consume substantially less power than incandescent light bulbs. However, typically, the radiant power of LED's has been limited so that they have been used for primarily short-range applications such as panel indicators or indoor signs. LED's have proven useful when their size has not been a significant factor because they are viewed from small distances. Unfortunately, use of LED's in outdoor applications such as traffic lights has been limited, due to high levels of ambient light. Even with the advent of "ultra-bright" LED's, large clusters of LED's are required to achieve adequate target-size definition. The longer distances involved in outdoor illumination devices, brighter ambient light conditions, and limits of resolution of the human eye are among factors which require clusters of large numbers of LED's in known systems. Unfortunately, these clusters are expensive and consume a considerable amount of power.
Various known systems have been involved in optically enhancing a light source. For example, U.S. Pat. No. 2,082,100 (Dorey et al.) discloses a light-spreading lens in which light radiating from a point source passes through a plate including several prismatic lenses to exit in a substantially parallel fashion. U.S. Pat. No. 2,401,171 (Leppert) discloses a traffic signal in which lamp light passes through a plurality of lenses before exiting the structure. Finally, U.S. Pat. Nos. 4,425,604 (Imai et al.) and 4,684,919 (Hihi) disclose illumination devices in which light reflects off elliptical surfaces or a plurality of prismatic surfaces before exiting.
Unfortunately, none of the known systems involve optimum use of light within the beam angle of LED's so as to provide signs of enough brightness for outdoor signs or traffic signals while still minimizing power consumption.